Overflowing classrooms are the reason the Belmont-Redwood Shores Elementary School District is going out for a $48 million facilities expansion bond measure on the November ballot.

The Board of Trustees approved the measure Tuesday to address the fact the district is expected to grow 20 percent in the next six years. All members voted yes, except for Trustee Robert Tashjian who recused himself from voting on the measure because he works for the Securities and Exchange Commission, which is a regulatory agency for bond sales.

“It’s a short timeline, so we’re having to do a fair amount of work in a limited amount of time,” said Superintendent Michael Milliken. “But we’ve put a lot of thought into these decisions and this work. We have a lot of confidence that our enrollment will grow in the next five to seven years.”

The district population has grown 42 percent over the last seven years and it is projected to add between 719 and 1,400 students in the next seven years, according to a spring study by demographic firm Lapkoff and Gobale. With this data, the Enrollment and Facilities Task Force found that the additional 719 students requires about 30 more classrooms, while 1,400 more students would mean 60 more classrooms. The staff proposes to plan construction in phases over several years to allow for facilities development to adjust to actual enrollment growth, according to a staff report.

In addition, the charge of $19.98 per $100,000 assessed property value would provide more classrooms for core academics such as science, math, reading and writing and preparing students for high school, college and 21st-century careers, officials said.

“This is something we don’t take lightly,” Milliken said. “It’s something we feel compelled to do.”

A district survey showed support from 65 percent of voters for a bond of $18 per $100,000 assessed property value. The Nov. 4 ballot measure requires 55 percent voter approval.

Last fall, Measure R, a consolidation of two parcel taxes, received 70 percent voter approval. The cost is $174 per parcel a year. Measure G, a $96 a year parcel tax for 10 years, passed in 2004. It generates about $1.2 million annually. In 2008, voters passed Measure U, a seven-year $78 annual tax that brings in about $950,000 per year. Measure R is a 10-year parcel tax starting July 1, 2015. In 2010, two bond measures were also approved by district voters, totaling $60 million for repairs, technology upgrades and bringing buildings up to code.

“We’re optimistic and encouraged by that support,” Milliken said. “We also know we have communicated and will have to communicate a rationale for the measure.”

Meanwhile, voter opinion research conducted in June indicates that community support for a bond to address school overcrowding is nearly 70 percent. The district says it’s also conducted community outreach in an effort to inform the community about consideration of a bond measure. Two mailers to all residents of the district and an email to parents of all school district students have been sent out in the last month. The correspondence invited the community to the Tuesday meeting.